OK, some advise for everyone. Read over ALL the comments before attempting to replace your iPhone 6 battery.
1. Don’t remove the screen cables or their shield, I didn’t, just hold it in your left hand (assuming your right handed) and focus on keeping the display perpendicular and open. When you’re tired or something, simply rest the screen again the body and open it again when needed!
2. Unhook the battery connector and bend it away as the FIRST thing you do and reconnect as the LAST thing.
3. My inner adhesive striped worked, my outer broke. I bent up the corner of the battery and fished out the white stuff with bent tweezers, then wrapped it around the tweezers and pulled, and wrapped, etc..it worked. Next time pulling the adhesive AROUND the permitter of the battery would have worked better!
4. The replacement battery is missing the foam pad on the top of the connector, reuse the one on from the old battery!
5. Dry-fit test and pre-bend the battery connector first, THEN add the adhesive and re-fit it.